The final segment of the intestine through which the meal traverses is the large intestine, which is composed of the cecum, colon, rectum, and anus. The primary role of the large intestine is to reclaim water used during the process of digestion and absorption and to store the residues of the meal until defecation is socially convenient.
2.
Colonic motility primarily serves to mix and delay passage of the luminal contents, other than during periodic large-amplitude contractions that convey fecal material to the rectum.
Bharucha AE, Brookes SJR. Neurophysiologic mechanisms of human large intestinal motility. In: Johnson LR, ed. Physiology of the GI Tract. 5th ed. Waltham, MA: Academic Press; 2012.
Bharucha AE, Hasler WL. Motility of the small intestine and colon. In: Podolsky DK, et al., eds. Yamada’s Textbook of Gastroenterology. 6th ed. Hoboken, NJ: Wiley Blackwell; 2015.
3.
The colon is highly active in transporting water and electrolytes as well as products salvaged from undigested components of the meal by colonic bacteria.
4.
The colon maintains a lifelong mutually beneficial relationship with a vast microbial ecosystem that metabolizes endogenous substances, nutrients, and drugs and protects the host from infection with pathogens.
5.
Defecation involves both involuntary and voluntary relaxation of muscle structures surrounding the anus and reflex pathways that control these structures.
Kau AL, et al. Human nutrition, the gut microbiome and the immune system. Nature. 2011;474:327-336.
Kendig DM, Grider JR. Serotonin and colonic motility. Neurogastroenterol Motil. 2015;27:899-905.
Koren A, Ley RE. The human intestinal microbiota and microbiome. In: Podolsky DK, et al., eds. Yamada’s Textbook of Gastroenterology. 6th ed. Hoboken, NJ: Wiley Blackwell; 2015.
Upon completion of this chapter the student should be able to answer the following questions: 1.
How does the liver contribute metabolic, detoxification, and excretory functions that are vital to life?
2.
What cell types make up the liver, what is their unusual arrangement, and what is the liver’s unique portal blood supply?
3.
What is the function of bile as an excretory fluid, what are the mechanisms that underlie its formation, and what is the role of the enterohepatic circulation?
4.
How is bile is stored and concentrated in the gallbladder, and what are the mechanisms that coordinate gallbladder emptying with ingestion of a meal?
5.
How are ammonia and bilirubin eliminated from the body?
Overview of the Liver and Its Functions